The present invention relates generally to high temperature thermal insulation and, more particularly, to a multilayered one-piece composite of thermal insulation formed of a layer of zirconia-bonded zirconia fibers joined to a layer of zirconia-bonded metal oxide fibers by a transition layer or zone formed of intermingled zirconia-bonded zirconia fibers and metal oxide fibers.
High temperature environments such as encountered in metallurgical furnaces, rocket propulsion nozzles and liners, and atmospheric reentry of aerospace vehicles require the use of thermal insulation capable of withstanding the high temperatures encountered while protecting nearby components from excessive heat.
A thermal insulation found to be highly satisfactory for use in applications where temperatures as high as about 2000.degree. C. are present is formed of zirconia fibers joined together in a zirconia matrix with the fibers being partially stabilized to maintain a cubic phase structure during temperature cycling. This thermal insulation is the subject of assignee's copending U.S. patent application Ser. No. 810,899 filed Dec. 20, 1985, and entitled "High-Temperature Zirconia Insulation and Method for Making Same." Inasmuch as the zirconia fibers, zirconia matrix, and zirconia stabilizing agents are the same or essentially the same as described and claimed herein and since the method utilized for molding the thermal insulation in assignee's application employ many similar steps, the aforementioned application is incorporated herein by reference.
While the zirconia fiber insulation described in assignee's above-identified application is a lightweight self-supporting insulation capable of providing highly desirable thermal insulating properties in high temperature environments, the cost of such insulation could be a drawback which detracts from its utilization in many applications. It has been found that a thermal insulation formed of essentially pure zirconia is required in environments having a hot face or surface subject to temperatures of about 2000.degree. C. However, the cost of the zirconia fibers with zirconia is relatively high as compared with insulation formed of metal oxide fibers such as alumina and silica.